A navy officer at the centre of allegations that asylum seekers suffered burnt hands on board a boat as it was turned back to Indonesia, says one asylum seeker burned his hand during an attempt to light a fire in the engine room.

Reports in January that asylum seekers had accused navy personnel of beating them and inflicting burns on them by making them hold hot engine parts drew an angry response and strong denials from the government.

New statements released by the Department of Defence and obtained by Guardian Australia present the first government account to be made public in relation to the allegations. They reveal that defence’s own investigation unit conducted a subsequent inquiry into the allegations.

The immigration minister, Scott Morrison, has refused to provide details about the allegations and any subsequent inquiries, citing the government’s policy of not discussing “on-water” matters.

In the statements, each of the navy officers said they were unaware of asylum seekers being harmed or mistreated in relation to the allegations.

One statement said an asylum seeker burned his left palm and added: “Burn associated with attempt to light fire in engine room.”

In an episode of the ABC’s 7.30 program aired in March, asylum seekers said there had been an attempt to sabotage the engine room after the relationship with defence personnel deteriorated.

Two of the statements also say that first aid was provided to the asylum seekers who were burned. In the 7.30 program asylum seekers said they were not given medical treatment until they returned to Indonesia.

Guardian Australia obtained the documents under freedom of information laws. In a highly unusual move, the defence department reversed its decision to refuse access to the documents following an application for review to the Office of the Australian Information Commission.

Defence initially refused access to all the documents, and said the statements “would only serve to compromise the effectiveness” of border operations.

Separate requests also show that the still camera seen being held by a navy officer on board the asylum seekers’ boat contains photographs from the operation at the centre of the allegations.

The existence of the statements also reveals that more substantial inquiries were made of defence personnel about the allegations, but raise further questions about the federal government’s reluctance to interview the asylum seekers involved.

The review officer said the facts in relation to the allegations “had been established and assessed multiples times” through operational reporting and a quick assessment.

He wrote that the allegations “cannot be substantiated” and there was “no requirements for further information” unless new additional information was forthcoming.

Guardian Australia asked the defence department whether any steps had been taken to take statements from the asylum seekers at the centre of the claims.

A spokeswoman for the defence department said: “The Australian Defence Force Investigative Service (ADFIS) conducted its own assessment of the allegations, including a review of the previous Quick Assessment and independent verification of relevant information.

“ADFIS also found that the allegations were not substantiated and that there was no requirement for further investigation unless new additional information was forthcoming.”

Morrison said at the time of the allegation that it was ‘’not for the government to disprove the negative, it’s for those who have allegations to actually prove the positive’’.

• This article was amended on 6 August 2014. The original incorrectly stated that the ABC’s 7.30 program aired in March was the report that Mark Scott said should have been “more precise”. This has been corrected.